Add yarn 0.24.6, remove yarn 0.24.5
Add yarn 0.24.6, remove yarn 0.24.5

source url: https://yarnpkg.com/downloads/0.24.6/yarn-v0.24.6.tar.gz
source sha256: 0019dfc4b32d63c1392aa264aed2253c1e0c2fb09216f8e2cc269bbfb8bb49b5

[#145961345]

ekaranto/rails4-bluemix-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,ekaranto/rails4-bluemix-buildpack,cloudfoundry/ruby-buildpack,ekaranto/rails4-bluemix-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,ekaranto/rails4-bluemix-buildpack